Among the participants, who were aged between 30 and 60 and followed over a number of years, a total of 306 cases of type 2 diabetes were reported. However, those drinking seven or more cups of coffee per day were half as likely to develop type 2 diabetes compared with participants who drank two cups or less a day.

This was even the case when factors like smoking, alcohol consumption and body mass were taken into account.

Type 2 diabetes is normally diagnosed in adults over the age of 50 and involves damage to the insulin-producing cells of the pancreas, usually as a result of unhealthy diet and lack of exercise.

Van Dam and Feskens say in their paper that while recent research has shown that caffeine acutely decreases the body's sensitivity to insulin, other ingredients in coffee - such as magnesium and chlorogenic acid - could actually help glucose metabolism.

"In view of the widespread use of coffee and the large health burden of type 2 diabetes, our findings of an inverse association between coffee consumption and risk of type 2 diabetes could have important public health implications," they write.

"However, possible adverse effects on other health aspects should be considered in the choice to consume coffee."

Alan Barclay of sufferer's support group Diabetes Australia, which funds some research and has looked into the implications of caffeine for diabetics, said the findings were "quite new and out of the blue".

However, he would not recommend people increase their consumption of coffee. "It's quite an extreme consumption level involved," he told ABC Science Online. "And research has shown that type 2 diabetes can be prevented by eating healthy foods and regular exercise."

An estimated 7.2 per cent of Australians over 25 suffer from diabetes, half of them undiagnosed. Type 2 diabetes represents 85 to 90 per cent of all cases of diabetes.